This invention relates to an apparatus and a method to deposit, polish, or electro-polish metal films on a substrate, or to remove such metal films from such a substrate. The unique anode assembly is particularly suitable for providing planar metal deposits on damascene-type interconnect and packaging structures.
Multi-level integrated circuit manufacturing requires many steps of metal and insulator film depositions followed by photoresist patterning and etching or other means of material removal. After photolithography and etching, the resulting wafer or substrate surface is non-planar and contains many features such as vias, lines or channels. Often, these features need to be filled with a specific material, such as a metal, a dielectric, or both. For high performance applications, the wafer topographic surface needs to be planarized, making it ready again for the next level of processing, which commonly involves deposition of a material, and a photolithographic step. It is most preferred that the substrate surface be flat before the photolithographic step so that proper focusing and level-to-level registration or alignment can be achieved. Therefore, after each deposition step that yields a non-planar surface on the wafer, there is often a step of surface planarization.
Electrodeposition is a widely accepted technique used in IC manufacturing for the deposition of a highly conductive material such as copper (Cu) into the features such as vias and channels opened in an insulating layer on the semiconductor wafer surface.
Electrodeposition is commonly carried out cathodically in a specially formulated electrolyte solution containing copper ions as well as additives that control the texture, morphology and plating behavior of the copper layer. A proper electrical contact is made to the seed layer on the wafer surface, typically along the circumference of the round wafer. A consumable Cu or inert anode plate is placed in the electrolyte solution. Deposition of Cu on the wafer surface can then be initiated when a cathodic potential is applied to the wafer surface with respect to an anode, i.e., when a negative voltage is applied to the wafer surface with respect to an anode plate.
The importance of overcoming the various deficiencies of the conventional electrodeposition techniques is evidenced by technological developments directed to the deposition of planar copper layers. For example, U.S. Pat. No. 6,176,992 to Talieh, entitled METHOD AND APPARATUS FOR ELECTROCHEMICAL MECHANICAL DEPOSITION, commonly owned by the assignee of the present invention, describes in one aspect an electro chemical mechanical deposition technique (ECMD) that achieves deposition of the conductive material into the cavities on the substrate surface while minimizing deposition on the field regions by polishing the field regions with a pad as the conductive material is deposited, thus yielding planar copper deposits.
U.S. application Ser. No. 09/740,701 entitled PLATING METHOD AND APPARATUS THAT CREATES A DIFFERENTIAL BETWEEN ADDITIVE DISPOSED ON A TOP SURFACE AND A CAVITY SURFACE OF A WORKPIECE USING AN EXTERNAL INFLUENCE, now U.S. Pat. No. 6,534,116, also assigned to the same assignee as the present invention, describes in one aspect a method and apparatus for plating a conductive material onto the substrate by creating an external influence, such as causing relative movement between a workpiece and a mask, to cause a differential in additives to exist for a period of time between a top surface and a cavity surface of a workpiece. While the differential is maintained, power is applied between an anode and the substrate to cause greater relative plating of the cavity surface than the top surface.
U.S. application Ser. No. 09/735,546 entitled METHOD AND APPARATUS FOR MAKING ELECTRICAL CONTACT TO WAFER SURFACE FOR FULL-FACE ELECTROPLATING OR ELECTROPOLISHING, filed on Dec. 14, 2000, now U.S. Pat. No. 6,482,307, describes in one aspect a technique for providing full face electroplating or electropolishing. U.S. application Ser. No. 09/760,757, entitled METHOD AND APPARATUS FOR ELECTRODEPOSITION OF UNIFORM FILM WITH MINIMAL EDGE EXCLUSION ON SUBSTRATE, filed on Jan. 17, 2001, now U.S. Pat. No. 6,610,190, describes in one aspect a technique for forming a flat conductive layer on a semiconductor wafer surface without losing space on the surface for electrical contacts.
In such above-mentioned processes, a pad or a mask can be used during at least a portion of the electrodeposition process when there is physical contact between the workpiece surface and the pad or the mask. The physical contact or the external influence affects the growth of the metal by reducing the growth rate on the top surface while effectively increasing the growth rate within the features.
In a metal deposition process using a soluble anode, it is necessary to minimize contamination of the deposited metal with anode sludge or anode fines. Typically, an anode bag is wrapped around the soluble anode to minimize this sort of contamination. In a conventional manner of copper electrodeposition for interconnect or packaging applications, as shown in FIG. 1, an anode bag or filter 150 is wrapped around an anode 152. A suitable space separates the anode 152 from the cathode 154 in the deposition cell 156. Agitation, recirculation or even filtration of the electrolyte solution 160 may be provided. During routine plating operations, anode sludge builds up in the anode sludge cavity 158 formed by the space between the anode 152 and the bag 150. In the case of Cu plating, excessive anode sludge build-up affects the quality of the deposited metal on the cathode 154 in an adverse manner. In particular, the uniformity of the deposited metal becomes poorer because of changes in the electric field distribution. In addition, the plating voltage increases because of anode polarization. The copper ions are unable to diffuse fast enough through the sludge layer to meet the requirements of the cathode. Moreover, the resulting loss in plating efficiency may cause hydrogen to be plated or evolve at the cathode. For routine maintenance, the anode 152 is removed from the deposition cell 156 and cleaned or desludged before replacement.
A general depiction of a plating and planarization apparatus in which improved anode assemblies such as those of the present invention can be used is shown in FIG. 2. The carrier head 10 holds a round semiconductor wafer 16 and, at the same time, provides an electrical lead 7 connected to the conductive lower surface of the wafer. The head can be rotated about a first axis 10b. The head can also be moved in the x and y directions represented in FIG. 2. An arrangement which provides movement in the z direction may also be provided for the head.
Certain embodiments of a carrier head that may be used to hold the wafer 16 form the subject matter of co-pending U.S. patent application Ser. No. 09/472,523, titled WORK PIECE CARRIER HEAD FOR PLATING AND POLISHING, filed Dec. 27, 1999, now U.S. Pat. No. 6,612,915, the disclosure of which is incorporated herein by reference as non-essential subject matter. Certain embodiments of anode assemblies with anode bags which are useable in conjunction with such a carrier head form the subject matter of co-pending U.S. patent application Ser. No. 09/568,584, filed May 11, 2000, titled ANODE ASSEMBLY FOR PLATING AND PLANARIZING A CONDUCTIVE LAYER, now U.S. Pat. No. 6,478,936, the disclosure of which is also incorporated herein by reference as non-essential subject matter.
A pad 8 is provided on top of a round anode assembly 9 across from the wafer surface. The pad 8 may have designs or structures such as those forming the subject matter of co-pending U.S. patent application Ser. No. 09/511,278, titled PAD DESIGNS AND STRUCTURES FOR A VERSATILE MATERIALS PROCESSING APPARATUS, filed Feb. 23, 2000, now U.S. Pat. No. 6,413,388. The disclosure of this co-pending application is also incorporated by reference herein as non-essential subject matter. Co-pending U.S. patent application Ser. No. 09/621,969, titled PAD DESIGNS AND STRUCTURES WITH IMPROVED FLUID DISTRIBUTION, filed Jul. 21, 2000, now U.S. Pat. No. 6,413,403, also relates to such pad designs and structures. The disclosure of application Ser. No. 09/621,969 is also incorporated by reference herein as non-essential subject matter.
The anode assemblies which are about to be described have the ability to rotate at controlled speeds in both directions and the mechanical strength to support a pad against which the wafer surface can be pushed with controlled force. They have the capability of receiving, containing, delivering, and distributing process fluids. The assemblies can be used for an electrodeposition process, as well as for a plating and planarization process or an ECMD process. The assemblies may even be used in a CMP tool.
This invention provides further improved anode designs and assemblies meeting the requirements of high quality metal plating and deposition of super-planar films. The special attributes of these further improved anode designs and assemblies are discussed below.
In each embodiment of the invention, an anode assembly by which a solution can be supplied to a surface of a semiconductor substrate includes a housing defining an internal housing volume into which the solution can flow. Each assembly also has a closure for the internal housing volume through which the solution can be discharged from the volume towards the substrate surface. A filter, by which the internal housing volume can be divided into a first chamber and a second chamber, is located between the first chamber and the closure. When the solution is being supplied to the surface, a flow of the solution into the second chamber occurs at a higher rate than a flow of the solution into the first chamber, and the flows are blended in the second chamber.
The housing includes at least one primary flow channel, through which the solution can pass directly into the second chamber, and at least one secondary flow channel, through which the solution can pass directly into the first chamber. In one embodiment, the primary and secondary flow channels are independent of each other. In an alternative embodiment, the secondary flow channel taps into the primary flow channel, and the secondary flow channel is adapted to divert a portion of the solution which flows through the primary flow channel to the first chamber.
The closure for the internal housing volume is a plate which can cover the volume. A pad through which the solution can flow lies over the plate.
A second filter can be provided between the second chamber and the closure. The second filter can have smaller pores than the first filter by which the internal housing volume can be divided into the first and second chambers.
In one embodiment of the invention, a drain by which sludge can be removed from the first chamber is provided. In a modified construction, an external filter, which pre-filters the solution before it enters the housing, can be utilized. In this case, the housing mentioned above is an upper housing, and the assembly further includes a lower housing, to which the external filter can be mounted, adapted to receive at least part of the upper housing in a volume defined thereby. In this construction, a fluid inlet chamber is defined between the lower housing and the upper housing when the lower housing receives this part of the upper housing.
An anode, usually a soluble anode, is typically received within the first chamber. The solution used, moreover, is typically an electrolyte solution out of which a conductive film can be deposited onto the surface of the semiconductor substrate.
According to another aspect of the invention, a process of supplying a solution to a surface of the semiconductor substrate received in the anode assembly includes providing the housing which has an internal volume. This volume is divided by a filter into a first chamber and a second chamber located between the first chamber and the surface. The solution is supplied to the housing, and is then divided into one flow passing directly into the second chamber and another flow passing into the second chamber through the first chamber. The flows are blended together in the second chamber, and the solution is then discharged from the housing towards the surface.
According to yet another aspect of the invention, at least one orifice can be used to remove air bubbles in the first chamber, in the second chamber, or in both the first and second chambers. At least one orifice in the first chamber and at least one orifice in the second chamber could be used to de-bubble the solution or prevent air bubble accumulation in the anode assembly. Air bubble accumulation may be reduced by way of a controlled leak between flanges.